A submarine exploring the ocean's depths recently returned with an unexpected visitor: a crablike critter called Bathynomus giganteus (commonly known as giant isopod).
This giant isopod (a crustacean related to shrimps and crabs) represents one of about nine species of large isopods in the genus Bathynomus. They are thought to be abundant in cold, deep waters of the Atlantic and Pacific oceans.

Photo of Bathynomus giganteus courtesy of NOAA Vents Program

In a posting to social bookmarking site Reddit, a deep-sea technician detailed finding the Bathynomus giganteus, asking the site's readers to help identify what exactly the bizarre-looking creature was.

The post reads, "I work for a Sub-sea Survey Company, recently this beast came up attached to one of our ROVs. It measures a wee bit over 2.5 feet head to tail, and we expect it latched onto the ROV at roughly 8,500 feet depth.

"Unfortunately, the e-mail that these pictures were attached to came from a contractor, and the ship he was operating from (and therefore location) is unknown, so I can't tell you what part of the Earth this beast was living."

The pictures reveal Bathynomus giganteus to be a giant isopod, a large crustacean that dwells in deep Atlantic and Pacific waters. This particular creature is a deep-sea scavenger that feeds on dead whales, fish and squid.

The underside of a male giant isopod.

Photo courtesy of NOAA/OER.

Scientists have long remarked on the massive scale of Bathynomus giganteus.

C.R. McClain, writing about Bathynomus giganteus explained one theory for the size, that "deep-sea gigantism, for all crustaceans, is a consequence of larger cells sizes obtained under cold temperatures," citing a research paper from 1996.

He also speculated that "in crustaceans, bathymetric gigantism may also in part reflect decreases in temperature leading to longer lifespans and thus larger sizes in indeterminate growers."